#define _CRT_SECURE_NO_WARNINGS 1

#include<iostream>
#include<cstring>
#include<queue>
#include<vector>

using namespace std;

typedef pair<int, int> PII;

const int N = 150010;

int h[N], w[N], e[N], ne[N], idx;
int dist[N];
bool st[N];
int n, m;

int dijkstra()
{
    memset(dist, 0x3f, sizeof dist);
    dist[1] = 0;

    priority_queue<PII, vector<PII>, greater<PII>> heap;
    heap.push({ 0,1 });

    while (!heap.empty())
    {
        auto t = heap.top();
        heap.pop();

        int ver = t.second, distance = t.first;
        if (st[ver]) continue;
        st[ver] = true;

        for (int i = h[ver]; i != -1; i = ne[i])
        {
            int j = e[i];
            if (dist[j] > distance + w[i])
            {
                dist[j] = distance + w[i];
                heap.push({ dist[j],j });
            }
        }
    }

    if (dist[n] == 0x3f3f3f3f)   return -1;
    else    return dist[n];
}

void add(int a, int b, int c)
{
    e[idx] = b, w[idx] = c, ne[idx] = h[a], h[a] = idx++;
}

int main()
{
    scanf("%d%d", &n, &m);
    memset(h, -1, sizeof h);
    for (int i = 0; i < m; i++)
    {
        int a, b, c;
        scanf("%d%d%d", &a, &b, &c);
        add(a, b, c);
    }

    cout << dijkstra() << endl;
    return 0;
}